The invention is relative to a waste-water installation with an inflow side for contaminated water and an outflow side for cleaned water and a cleaning device arranged between them for retaining or separating impurities delivered on the inflow side, and with a damming element arranged after the cleaning device. Such waste-water installations are used to drain off the increased amount of rainwater that accumulates during rather heavy precipitations since it can no longer be managed, e.g., by a sewage treatment plant. However, the increased amount of accumulating rainwater is mixed with contaminated water, so that it is contaminated with suspended material, e.g., pieces of wood, sand, paper or plastic foils. These contaminants (impurities) are removed or retained from the rainwater and diverted, e.g., into a body of water, by such waste-water installations by means of a cleaning device, e.g. a sieve (screen) rake. The above-mentioned cleaning device is arranged between the inflow area of the waste water and the outflow area from which the rainwater drained off for removal of the load (relief) is conducted away. Such a device is known from WO 94/07585.
The device shown in this document comprises an intermediate wall between the inflow side and the outflow side, on which wall a cleaning device in the form of a sieve rake is arranged. In addition to the action of the intermediate wall, a damming element inclined to the vertical plate is provided in the direction of flow behind the sieve rake in order to increase the damming volume of retained water upstream of the sieve rake. This arrangement should help to even out the flowthrough rate of the water through the sieve rake and obtain a more uniform distribution of pressure over the entire surface of the sieve rake. However, the device shown has the disadvantage that in particular suspended material and sinking (settling) material such as, e.g., sand, can not overcome the inclined damming element so that they remain in the area of the sieve rake and cause problems there, especially for the rake cleaner. The remaining sinking material causes increased wear between the sieve rake and the rake cleaner. In addition, the damming element does increase the retention capacity of the waste-water installation, but if the damming element is flooded, the damming element forms a throttling device so that the flowthrough amount through the rake is reduced and there is the danger that the sieve rake is flooded above its upper edge, as a result of which unpurified water is removed.
The present invention aims to avoid the cited disadvantages of the known waste-water installations and also not to hinder the flowthrough through the cleaning device of the waste-water installation in spite of the elevation of the damming volume.